This invention relates to an electrode for electrical discharge machining which is applied to perforation or other working on a material by means of electron discharge from the electrode.
In recent years, electrical discharge machining has attracted considerable attention because it can be applied to a field in which a prior art machine tool can not be applied or to a complicated precision machining which offers difficulties when a machine tool is used. It is desired that electrical discharge machining satisfy the following requirements:
(1) High machining speed
Machining speed is generally defined as follows: ##EQU1##
Generally, the speed of electrical discharge machining is extremely low due to its mode of operation; it is as low as the grinding speed of a machine tool. Since the demand for electrical discharge machining is increasing the increase of late, it is desired to increase the machining speed.
(2) Low electrode consumption
As one of factors determining electrode consumption, the following electrode consumption rate is defined herein as: ##EQU2##
The lower the electrode consumption rate, the smaller the electrode consumption required for a fixed amount of machining of the material. In other words, the lower electrode consumption rate leads to the longer life of the electrode. The electrode is also locally deformed by electrode consumption leading, as for example, to corner wear that results in the tapering of the machined portion resulting in errors in the product shape. This also accounts for importance of lowness in the electrode consumption.
(3) Accuracy of machining
The clearance should be uniform between the electrode surface and the machined surface of the material. Uniform clearance means that machining is performed accurately. This requirement is concerned partly with requirement (2) as known from the description contained herein.
(4) Smoothness of the machined surface
To satisfy this condition, the electron discharge from the electrode should be stable. Unstable electron discharge not only lowers the machining speed and creates tapering, but also makes the machined surface nonuniform and coarse.
To perform electrical discharge machining satisfying the above requirements, improvements in electrode conposition play a vital role as well as improvements in machining processes.
Electrodes for electrical discharge machining which have been practically used are roughly classified into those consisting chiefly of carbon (C), those consisting chiefly of copper (Cu), and those based on tungsten (W). Electrodes consisting chiefly of C or Cu can be manufactured cheaply, but are not suitable for use in precision machining because they have an excessive electrode consumption rate.
W-Cu electrode and W-Ag electrode are known as typcial examples of W-based electrode. They advantageously have low consumption rate, but adversely provide low machining speed. It is therefore desired to obtain a W-based electrode having satisfactory properties, particularly with respect to machining speed. Recently, new electrodes are offered which are prepared by adding thoria (ThO.sub.2) to W-Cu or -Ag alloys. The electrode bears properties suitable for electrical discharge machining. The problem, however, is that ThO.sub.2 is radioactive, and is difficult and cumbersome to handle.
An object of this invention is to provide an electrode for electrical discharge machining satisfying the above-mentioned requirements.
Another object is to provide an improved W-based electrode for electrical discharge machining.
The other objects will be apparent from the following descriptions.
These and other objects of the invention are attained by the electrode which is formed of a tungsten-based alloy including 15 to 40% by weight of one memeber selected from the group consisting of Ag, Cu and a mixture thereof, and 0.5 to 10% by weight of ZrO.sub.2.